Sevoflurane requirement to maintain bispectral index-guided steady-state level of anesthesia during the rewarming phase of cardiopulmonary bypass with moderate hypothermia

Abstract

Objectives: The authors aimed to quantify any increase and the extent of the increase in sevoflurane requirements for maintaining hypnosis during hypothermic cardiopulmonary bypass (CPB) with the bispectral index (BIS) maintained between 40 and 50. Design: An observational prospective study. Setting: A single-center tertiary referral center at a university hospital. Participants: Fifty patients undergoing elective coronary artery bypass graft surgery with CPB. Interventions: End-tidal oxygenator expiratory gas concentrations were used to quantify sevoflurane requirements while maintaining a BIS level between 40 and 50 during the rewarming phase. Results: Sevoflurane requirements progressively increased as temperature increased. The difference in sevoflurane requirement at 35°C and 29°C was compared using analysis of variance for repeated measures, which was statistically significant. When relating temperature and sevoflurane requirement, the Pearson correlation coefficient was 0.67. Linear regression analysis using temperature as the independent variable and expiratory sevoflurane as the dependent variable showed a temperature β-coefficient of 0.11 and a constant of -2.34. Other parameters like fresh gas flows and pump flows were correlated to find out if they affected end-tidal sevoflurane levels on CPB. They were not significant in multivariate analysis. Conclusions: The sevoflurane requirement increases during the rewarming phase of hypothermic CPB. The percent increase in the requirement for sevoflurane is uniform and follows a particular pattern, which may be predicted. © 2012 Elsevier Inc.